Method and an assembly for braking a selectively moveable assembly having a controllably varying amount of self energization

ABSTRACT

A brake assembly including a brake pad; a selectively movable rotor, a backing plate which is coupled to the brake pad, at least a first roller which is coupled to the backing plate, a caliper, at least a second roller which is coupled to the caliper, a wedge member which is positioned between and which engages the at least first and the at least second roller, and a motor which is coupled to the wedge member and which selectively moves the wedge member, effective to brake a selectively movable assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/063,635filed May 6, 2002, now issued as U.S. Pat. No. 6,752,247.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method and an assembly forbraking a selectively movable assembly and more particularly, to avehicular brake assembly which provides a controllably varying amount ofself energization and to a method for braking a selectively movableassembly which provides this controllably varying amount of selfenergization by the use of a pair of selectively movable wedge memberswhich cooperatively allow a vehicle to be smoothly and efficientlybraked with the use of a pair of relatively small electrical motors.

2. Background Art

An electromechanical braking assembly typically 20 provides braking of aselectively movable assembly (such as a vehicle) by the use of a motorwhich becomes selectively energized upon a sensed depression of a brakemember. At the outset, it should be appreciated that the term“selectively movable assembly” refers to any assembly, including but notlimited to a vehicle, which has at least one wheel which may beselectively rotated and which must be selectively braked. Hence, itshould be realized that the present invention is applicable to a widevariety of such selectively movable assemblies and is not limited onlyto a vehicle. Further, while the terms “vehicle” and “selectivelymovable assembly” may be interchangeably used in this description, thepresent invention is not limited to a vehicle or any other particulartype of selectively movable assembly.

Particularly, such an electromechanical braking assembly typicallyincludes a rotor which moves with the wheel of the vehicle or otherselectively movable assembly in which the electromechanical brakingassembly is operatively disposed and a pad which is made to engage therotor, by the selectively activated motor, effective to brake the movingwheel and thereby brake the selectively movable assembly. Importantly,such an electromechanical braking assembly does provide some advantagesover traditional hydraulic brake systems. One non-limiting example ofsuch an electromechanical brake assembly is described within EuropeanPatent Number EP 0953785A3 which is fully and completely incorporatedherein by reference, word for word and paragraph for paragraph.

By way of example and without limitation, such an electromechanicalbraking system provides the desired braking in a substantially shorteramount of time than that which is provided by a conventional hydraulicbraking system and allows each of the individual wheels of a vehicle orother selectively movable assembly to be selectively controlled, therebyenhancing the effectiveness of many operating strategies such as ananti-skid or anti-lock braking strategy or a strategy which is commonlyreferred to as an “integrated vehicular dynamic” strategy.

However, while such an electromechanical braking system provides theseand other advantages, it requires a relatively large motor whichincreases the overall cost of producing the vehicle (or otherselectively movable assembly) while concomitantly and undesirablyrequiring a relatively large packaging space which may require amodification in the packaging design of many assemblies, such as vehicleassemblies, which have respectfully and relatively “tight” spaceconstraints or requirements. Further, the relatively large motorrequires a relatively large amount of electrical power in order tooperate, thereby requiring a relatively large battery or power source,in excess of that which is conventionally placed within a vehicle,thereby further and undesirably increasing the overall production costof the vehicle or other selectively movable assembly.

Further, current electromechanical brake systems utilize only a singlemotor and this architecture may be undesirable since these systems maynot provide a desired amount of braking in the event that the singleprovided motor is not activated. In contrast to the “single motor”electromechanical braking system, an electro-hydraulic braking systemnormally utilizes a manual second or “back up” braking assembly whichbrakes the vehicle or other selectively movable assembly in the event ofthat desired braking is not provided by the “primary” electro-hydraulicbraking assembly. Although this approach does provide the desiredredundancy, it undesirably increases the cost of producing the vehicle,undesirably increases the amount of required packaging space, and, asearlier delineated, does not provide all of the features and benefitsassociated with an electromechanical braking system.

One attempt to overcome these drawbacks requires the use of aself-energization member, having at least one or more substantiallyidentical wedges which are deployed upon or provided by a single wedgemember, and which is typically deployed within the electromechanicalbraking system. Particularly, the at least one wedge (as well as theother wedges) has a fixed angle of inclination that provides additionalmechanical advantage and assists in “forcing” the brake pad against therotor, thereby reducing the amount of braking actuation power which mustbe provided by the motor. Importantly, it is the shape or geometricconfiguration of the at least one wedge which assists the motor inbraking the assembly, thereby conserving energy (e.g., the physical ormechanical properties of the at least one wedge provide this desired“brake enhancing” functionality without requiring additional activationenergy or power from the motor). Hence, a member which “provides” such awedge is referred to as a “self-energization” member. While thisapproach does reduce the overall power requirements and the size of themotor, it too has several drawbacks.

For example and without limitation, a conventional electromechanicalself-energizing braking system provides a fixed amount ofself-energization (an amount which is not selectively variable by acontrolled amount and which is wholly determined by the fixed angle ofinclination of the at least one wedge as the selectively movableassembly moves in a certain direction), even though the amount offriction between the rotor and the pad varies with temperature,humidity, and other environmental conditions. Therefore, thisarrangement requires the operator of the selective moving assembly tovary the amount of pressure or force which is exerted on the brakingmember in order to achieve the same amount of braking as theseenvironmental conditions change during the operation of the selectivelymovable assembly, thereby undesirably causing the operator to have aninconsistent braking “feel”. Further, this approach does not allow forthe use of a relatively low powered motor since the motor must becapable of operating under conditions in which the amount of frictionbetween the rotor and the pad is relatively high and when the amount offriction between the rotor and the pad is relatively low. The inabilityof the motor to operate under these extreme frictional conditions mightcause the brake assembly to undesirably enter a tension mode (e.g., amode in which the motor must overcome the friction force which ispulling the pad in the same direction as the rotor is moving in order toreduce braking force) from a desired compression mode (e.g., a mode inwhich the motor pushes the pad in the same direction as the rotor ismoving in order to generate a brake force).

That is, during a compression mode of operation which occurs when thefrictional force is relatively low, an “undersized motor” (e.g., a motorwhich does not provide enough actuation force to ensure desiredoperation in high and low friction conditions) may not be capable ofgenerating the deceleration desired by the operator. During a tensionmode of operation, which occurs when the frictional force is relativelyhigh, an “undersized motor” may not be able to pull the pad with enoughforce to prevent it from being frictionally “locked” onto the rotor,thereby preventing the braking assembly from providing the desiredbraking required by the operator.

Further, while the current electromechanical braking configuration, inthe desired compression mode, provides a high gain at one level offriction (e.g., during high friction), it will provide a much lower gainat lower friction levels. This means that a larger actuating motor mustbe utilized than would be necessary if the wedge angle or the angle ofinclination could be “optimized” (i.e., dynamically configured toprovide large amounts of brake enhancement at each friction level).Hence, due to the use of a fixed amount of self-energization (emanatingfrom the use of a fixed angle of inclination), a relatively large motormust be employed to ensure that the braking assembly functions during“worst case” situations in which a large amount of activation power isrequired.

Moreover, yet additional drawbacks exist if a single and relativelysmall motor were utilized in a conventional electromechanical brakingsystem which is designed to operate in both the compression mode and thetension mode. That is, the relatively small motor must overcome theinertia associated with existing compression braking in order to providetension type braking, thereby resulting in a relatively slow responsetime which provides an uncomfortable “feel” to the operator of theselectively movable assembly. Moreover, the braking assembly, inovercoming such inertia, may even provide an undesirable amount ofcompression or tension type force. In fact, at one instant of time,during this transition, the motor neither provides compression nortension and at this “zero point”, the braking assembly may not functionin a desired manner.

The present invention overcomes these drawbacks in a new and novelfashion by allowing for a controllably varying amount ofself-energization to occur as the amount of friction between the rotorand the pad varies.

SUMMARY OF THE INVENTION

It is a first non-limiting advantage of the present invention to providea braking assembly which overcomes some or all of the previouslydelineated disadvantages of prior braking assemblies.

It is a second non-limiting advantage of the present invention toprovide a method for braking a selectively movable assembly whichovercomes some or all of the drawbacks associated with prior brakingmethods.

It is a third non-limiting advantage of the present invention to providean electromechanical braking assembly having a controllably varyingamount of self-energization.

It is a fourth non-limiting advantage of the present invention toprovide a brake assembly including a pair of selectively movable memberseach having a respectively unique angle of inclination; and a controllerassembly which selectively causes the pair of selectively movablemembers to cooperatively provide a controllably varying amount of selfenergization.

It is a fifth non-limiting advantage of the present invention to providea brake assembly comprising a brake pad; a selectively movable rotor; abacking plate which is coupled to the brake pad; at least a first rollerwhich is coupled to the backing plate; a caliper; at least a secondroller which is coupled to the caliper; a wedge member which ispositioned between and which engages the at least first and the at leastsecond roller; and a motor which is coupled to the wedge member andwhich selectively moves the wedge member, effective to brake aselectively movable assembly.

It is a sixth non-limiting advantage of the present invention to providea method for braking a vehicle of the type having at least oneselectively movable wheel. Particularly, the method includes the stepsof providing a rotor; coupling the rotor to the at least one wheel;providing a backing plate; providing at least one brake pad; couplingthe at least one brake pad to the braking plate; providing a firstwedge; coupling the first wedge to the brake pad; providing a secondwedge; movably coupling the second wedge to the first wedge; providing afirst and a second motor; coupling the first motor to the first wedge;coupling the second motor to the second wedge; causing the first motorto move the first wedge against the second wedge and against the brakepad, effective to cause the brake pad to frictionally engage the rotor,thereby braking the vehicle.

These and other features and advantages of the present invention willbecome apparent from a reading of the following detailed description ofthe preferred embodiment of the invention and by reference to thefollowing drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective and partially cut away view of anelectromechanical braking assembly which is made in accordance with theteachings of the preferred embodiment of the invention;

FIG. 2 is a block diagram of the electromechanical braking assemblywhich is shown in FIG. 1;

FIG. 3 is a block diagram of an electromechanical braking assembly whichis made in accordance with the teachings of an alternate embodiment ofthe invention;

FIG. 4 is a block diagram of an electromechanical braking assembly whichis made in accordance with the teachings of a second alternateembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIGS. 1 and 2, there is shown an electromechanicalbrake assembly 10 which is made in accordance with the teachings of thepreferred embodiment of the invention.

Particularly, the electromechanical brake assembly 10 includes at leastone rotor 12 which is attached to and which selectively rotates with awheel (not shown) of the selectively movable assembly or vehicle (notshown) into which the brake assembly 10 is operatively disposed within.Further, as shown, the electromechanical brake assembly 10 includes atleast one pad member 14 which may selectively engage the movable rotor12 in a manner which is more fully delineated below and which iseffective to brake the selectively movable assembly which operativelycontains the electromechanical brake assembly 10. It should beappreciated that multiple pad members 14 may be used within the brakeassembly 10 and that a selectively movable assembly, such as a vehicle,may have one brake assembly 10 operatively disposed on each selectivelymovable vehicular wheel.

Further, the electromechanical brake assembly 10 includes a backingplate 16 which is physically connected or coupled to the pad member 14,a caliper assembly 18 which is coupled to the body or frame 20 of theselectively movable assembly which operatively contains assembly 10, amember 22, such as a pin, bearing, dowel or slide, which is physicallyconnected or coupled to the caliper 18 (e.g., by use of a welded orother conventional connection), a first self energization member orwedge member 24 having at least one wedge or wedge portion 25 and whichis physically connected or coupled to the backing plate 16, a secondself energization member or wedge member 26 which has at least one wedgeor wedge portion 27 which is selectively and engagably received by thefirst wedge portion 25, a first motor 30 which includes an output shaft35 which selectively engages the first wedge member 24, a second motor34 having an output shaft 36 which selectively engages the second wedgemember 26, a computer controller 40 which is operable under storedprogram control and which is physically, communicatively, andcontrollably coupled to the first and second motors 30, 34 by the use ofrespective busses 44, 46, and a source of electrical power 50 (e.g., avehicular battery) which is physically coupled to the controller 40 bythe use of bus 52. In the preferred embodiment of the invention, caliper18 “covers” approximately a sixty to ninety degree area of the rotor 12,(i.e., the caliper 18 circumscribes an angle of approximately 60 to 90degrees of the rotor 12). However, it should be understood to one who isskilled in the relevant art that caliper 18 may be substantially anydesired configuration or cover substantially any desired angular portionof rotor 12.

The braking assembly 10 further includes an accelerometer 61 which isphysically and communicatively coupled to the controller 40 by use ofthe bus 63. The controller 40 is further communicatively coupled to aselectively depressible brake member or pedal 41 by the use of bus 43.The controller 40 and motors 30, 34 may comprise a “controller assembly”and, in one non-limiting embodiment, motors 30, 34 are substantiallyidentical.

In operation, the brake member 41 is depressed by an operator of theselectively movable assembly when the operator desires to decelerate orbrake the selectively movable assembly. Upon the detection of thedepression of the brake member 41, the controller 40 determines that acertain amount of braking is desired. That is, in one non-limitingembodiment, a calibrated table having several brake member positions andrespective amounts of braking are stored within the controller 40. Abraking value is selected by use of the table (e.g., the braking valueof the stored brake position which is closest to the currently sensedposition is selected from the stored table). The controller 40 thenactivates the motor 30, thereby causing the shaft 35 to engage wedgemember 24, effective to force the at least one wedge portion 25 againstthe at least one wedge portion 27 of the member 26 and this forces theat least one wedge member 26 against frame mounted caliper 18 throughmember 22 and causes a braking force to be executed on the brake pad 14by the member 24, effective to initially supply a certain and relativelysmall amount of braking to the selectively movable assembly whichoperatively contains assembly 10.

The accelerometer 61 then senses the rate of deceleration of theselectively movable assembly that the brake assembly 10 is operativelydisposed within and uses this sensed rate of deceleration to determinethe amount of friction which is present or which currently existsbetween the brake pad 14 and the rotor 12. This determination isachieved in the manner which is more fully discussed below.

Particularly, as shown, the at least one wedge portion 27 of member 26has an angle of inclination 62 while the at least one wedge portion 25of member 24 has an angle of inclination 60. Once the member 24 isinitially moved in response to the initial sensing of the depression ofmember 41, a wedge or self energization angle “α” may be calculated byuse of the following equation: $\begin{matrix}{{{Tan}\quad(\alpha)} = {\frac{\left( {{input}\quad{force}} \right)\quad\mu}{\left( {{output}\quad{force}} \right)} + \mu}} & \left( {{Equation}\quad 1} \right)\end{matrix}$

-   -   where:    -   “μ”=coefficient of friction between the brake pad 14 and the        rotor 12;    -   “output force”=frictional force acting on the rotor 12; and    -   “input force” force provided by motor 30 acting on the wedge        member 24 which may be sensed (e.g., by use of a force sensor        which is coupled to the motor 30) or easily measured by the        controller 40.

The “output force” may be calculated by the controller 40 as a frontoutput force and a rear output force as follows:output force (front)=0.5*F×b×R _(t) /R _(c)  (Equation 2)output force (rear)=0.5*F×(1−b)×R _(t) /R _(c)  (Equation 3)

-   -   where:    -   “F”=the decelerative force which is measured by the        accelerometer 61;    -   “R_(t)” is the radius of the tire which is attached to the wheel        upon which brake assembly 10 is operatively disposed (not shown)        and which may be easily measured;    -   “R_(c)” is the effective radius of the caliper 18 which may be        easily measured; and    -   “b” is the percentage of total braking force which is supplied        by the front tires and which may be measured or sensed by the        controller 40. Hence, by knowing the initial angle “α”, which        may be determined by the controller 40 by identifying the wedge        member which is initially moved (e.g., the variable “α” is equal        to the value of angle 60 when wedge 24 is moved), the value of        “μ” may be easily determined by the controller 40. Thus, the        amount of friction between the brake pad 14 and rotor 12 may        then be ascertained by the controller 40.

Particularly, in high friction conditions, the second motor 34 is notactivated and the wedge member 26 is substantially stationary. The firstmotor 30 continues to be activated by the controller 40, effective tocause the output shaft 35 to move the wedge member 24 and causing thewedge portion 25 of member 24 to engage the member 26 (to engage portion27), thereby providing self energization since the angle 60 of the wedgeportion 25 of the wedge member 24 causes or forces the wedge portion 27of the wedge member 26 to engage member 22 and causes member 24 toprovide force onto the brake pad 14. It should be realized that thefirst motor 30 is activated upon receipt of electrical power which issourced from the power supply 50 and communicated to the first motor 30by the use of busses 52, and 44. Alternatively, motors 30, 34 may bothbe activated in order to actuate the wedge members 24, 26 in oppositedirections, thereby providing both force upon the brake pad 14 and selfenergization in substantially high friction environments.

In relatively low friction environments (associated with a certain rateof deceleration) which are sensed by the controller 40 in the foregoingmanner or conditions, both of the motors 30 and 34 are activated,thereby causing the output shafts 35 and 36 to move wedge members 24, 26in substantially the same direction, thereby providing an overall lowerangle of inclination (e.g., the effective angle of inclination isrelatively small and is equal to the difference between angle 60 and62).

In the forgoing manner, the electromechanical brake assembly 10 providesa controllably varying amount of self energization effective to allowthe brake assembly 10 to always provide a substantially large amount ofself energization even under varying environmental conditions. Thusmotors 30, 34 may each be relatively small and cooperatively provide aredundant braking architecture, since the braking assembly 10 mayoperate with only one of the motors 30, 34. In one non-limitingembodiment, the foregoing frictional measurements and calculations maybe periodically accomplished by the controller 40 as the brake assembly10 is being operated and, based upon these calculations, the controller40 may dynamically control motors 30, 34 to dynamically vary the amountof provided self energization in a controlled manner.

In yet another non-limiting embodiment of the invention, an intermediategear assembly, such as gear assembly 38, may be coupled to either/bothof the output shafts 35, 36, and a screw actuator assembly, such asscrew actuator assembly 39, is coupled to each assembly 38. As shown inFIG. 2, a pair of assemblies 38, 39 cooperatively transfers energy froma shaft 35, 36 to a member 24, 26. It should be understood that manydifferent actuation means or devices may be employed to actuate thewedge members 24, 26 and that nothing in this description is meant tolimit the present assembly 10 to include the assemblies 38, 39.

Referring now to FIG. 3, there is shown a brake assembly 100 which ismade in accordance with the teachings of a first alternate embodiment ofthe invention. Particularly, brake assembly 100 differs from brakeassembly 10 in that wedge members 24 and 26 are replaced by a single“V”-shaped wedge 102, the member 22 is replaced with a roller member 104contacting the upper surface of wedge 102, and two substantiallyidentical roller members 106 are attached to the backing plate 16 andprotrude from the baking plate 16 in a direction toward the wedge member102 to contact the lower surface of wedge 102. As shown in FIG. 3, theupper and lower surfaces of wedge 102 are at different angles and themovement of the pad 14, backing plate 16, and roller 106 by motor 30selectively forces brake pad 14 against the rotor 12. That is, thebottom wedge angle of wedge member 102 is utilized by motor 30 toprovide self energization in relatively high friction environments. Inrelatively low friction environments, motors 34, 30 may both beactivated to actuate both the wedge member 102 (i.e., by use of motor34) and the backing plate 16 (i.e., by use of motor 30) in order to movethe wedge member 102 in substantially the same direction as the backingplate 16. Alternatively, in substantially high friction environments,motors 30, 34 may be activated in order to actuate the wedge member 102in a substantially opposite direction as the backing plate 16. It shouldbe understood that in this first alternate embodiment of the invention,the backing plate 16 is actuated in substantially the same manner as thewedge member 24 of the preferred embodiment.

The use of rollers 104 and 106 reduces friction by eliminating and/orreducing the amount of friction which typically occurs between themember 22 and the wedge member 24 and by eliminating and/or reducing theamount of friction which occurs between the wedges members 24, 26. Suchreduced friction allows the motors 30, 34 to be even smaller than thoseused in the embodiment which is shown and described with respect toFIGS. 1 and 2. In one non-limiting embodiment, roller member 104 may besubstantially identical to roller member 106.

Referring now to FIG. 4, there is shown a brake assembly 200 which ismade in accordance with the teachings of yet another embodiment of theinvention and which differs from the brake assembly 100 in that tworollers 202, 204 are used instead of the single roller 104 and fourrollers 206, 208, 210, and 212 are used instead of the rollers 106. Theuse of these rollers 206-212 not only reduces friction but ensures thatthe pad 14 remains substantially parallel to the rotor 12, therebyeliminating taper wear.

It is to be understood that the invention is not limited to the exactconstruction which has been delineated above, but that various changesand modifications may be made without departing from the spirit and thescope of the inventions as they are delineated in the following claims.

1. A variable self-energization system for a brake assembly having acaliper, a rotor, and a brake pad, the self-energization systemcomprising: a first self-energization member movably mounted to thecaliper and having a first working surface with a first angle ofinclination and a second working surface generally opposite the firstsurface and with a second angle of inclination, the first and secondangles of inclination both being non-zero and being different from oneanother such that the first and second working surfaces are non-parallelwith one another; a reaction member mounted to the caliper andcontacting the first working surface; a second self-energization membercontacting the second working surface; and a controller assemblycomprising a first motor connected to the first self-energization memberand operative to move the first self-energization member, a second motorconnected to the second self-energization member and operative to movethe second self-energization member, and a controller controlling thefirst motor and the second motor; whereby said motion of the first andsecond self-energization members causes the first self-energizationmember to be displaced in a direction which varies a force applied bythe brake pad to the rotor.
 2. The system of claim 1 wherein the firstself-energization member is “V”-shaped.
 3. The system of claim 1 whereinthe reaction member orthogonally projects from the caliper and comprisesat least one roller.
 4. The system of claim 1 wherein the secondself-energization member comprises a second wedge member.
 5. The systemof claim 1 wherein the second self-energization member projectsorthogonally from a backing plate that is coupled to the brake pad andcomprises at least one roller.
 6. The system of claim 5 wherein thereaction member comprises at least two rollers and the secondself-energization member comprises at least four rollers.
 7. A variableself-energization system for a brake assembly having a caliper, a rotor,and a brake pad, the self-energization system comprising: a reactionmember mounted to the caliper; a first self-energization member mountedto the caliper and movable relative to the caliper and having a firstworking surface contacting the reaction member and a second workingsurface disposed generally opposite the first working surface, the firstand second working surfaces being non-parallel with one another; asecond self-energization member mounted to the caliper and movablerelative to the caliper and contacting the second working surface; and acontroller assembly comprising a first motor connected to the firstself-energization member and operative to move the firstself-energization member, a second motor connected to the secondself-energization member and operative to move the secondself-energization member, and a controller controlling the first motorand the second motor; whereby motion of the first self-energizationmember relative to the caliper causes the first self-energization memberto be displaced in a direction which varies a force applied by the brakepad to the rotor.
 8. The system of claim 7 wherein the firstself-energization member is “V”-shaped.
 9. The system of claim 7 whereinthe reaction member orthogonally projects from the caliper and comprisesat least one roller.
 10. The system of claim 7 wherein the secondself-energization member comprises a second wedge member.
 11. The systemof claim 7 wherein the second self-energization member projectsorthogonally from a backing plate that is coupled to the brake pad andcomprises at least one roller.
 12. The system of claim 11 wherein thereaction member comprises at least two rollers and the secondself-energization member comprises at least four rollers.